Culturally transmitted song exchange between humpback whales (Megaptera novaeangliae) in the southeast Atlantic and southwest Indian Ocean basins.

Melinda L Rekdahl,Ellen C Garland,Tim Collins,Howard Rosenbaum,Carissa D King,Gabriella A Carvajal,Yvette Razafindrakoto

doi:10.1098/rsos.172305

Abstract

In migratory marine species, investigating population connectivity and structure can be challenging given barriers to dispersal are less evident and multiple factors may influence individual movement patterns. Male humpback whales sing a song display that can provide insights into contemporary connectivity patterns, as there can be a cultural exchange of a single, population-wide shared song type with neighbouring populations in acoustic contact. Here, we investigated song exchange between populations located on the east and west coasts of Africa using 5 years of concurrent data (2001–2005). Songs were qualitatively and quantitatively transcribed by measuring acoustic features of all song units and then compared using both Dice’s similarity index and the Levenshtein distance similarity index (LSI) to quantitatively calculate song similarity. Song similarity varied among individuals and potentially between populations depending on the year (Dice: 36–100%, LSI: 21–100%), suggesting varying levels of population connectivity and/or interchange among years. The high degree of song sharing indicated in this study further supports genetic studies that demonstrate interchange between these two populations and reinforces the emerging picture of broad-scale connectivity in Southern Hemisphere populations. Further research incorporating additional populations and years would be invaluable for better understanding of fine-scale, song interchange patterns between Southern Hemisphere male humpback whales.

Highlights

Population structure and connectivity among populations are important factors to consider in conservation and management decisions [1,2,3,4]
We investigated the degree of song sharing between the Gabon and Madagascar populations across five concurrent years (2001 –2005) to investigate: (i) whether song sharing occurs between the Gabon and Madagascar populations, which have a relatively high level of genetic mixing (12 –14), (ii) the degree to which songs are shared and how this varies over time, and (iii) whether measures of song similarity can be used to relate song sharing with population connectivity patterns, as observed in other Southern Hemisphere populations
Our study continues to reinforce the use of acoustic methods to investigate humpback whale population connectivity, and we advocate the use of this method to support genetic and photo-identification studies

Summary

Introduction

Population structure and connectivity among populations are important factors to consider in conservation and management decisions [1,2,3,4]. A number of factors may influence population structures in migratory marine species, including ecological, environmental, genetic and behavioural processes, which may operate over historical or contemporary time scales [7]. While the fields of genetics and more recently genomics [10] have proved invaluable for understanding population structure and connectivity of marine mammals over historical time scales, limitations exist for interpreting contemporary movement and connectivity patterns using these methods. Using additional methods that can contribute behavioural and/or environmental information at a higher temporal resolution can prove beneficial for informing conservation and management decisions [11]

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Results

Conclusion